Untitled

Abstract

The sorption behavior of Cs + on kaolinite, chlorite-illite, and bentonite clays as a function of time, cation concentration, and temperature was studied using the radiotracer method. Sorption data were well represented by Freundlich and Dubinin-Radushkevich type isotherms. Bentonite was found to have the highest sorption capacity and the highest exchange affinity to Cs + . In all three cases Cs + sorption was found to be exothermic with ∆H° (kJ/mol) -13, -8, -19 and ∆S° (J/mol . K) -15, 31, and -3 for kaolinite, chlorite-illite, and bentonite, respectively. Negative ∆G° values were obtained in all cases, indicating the spontaneity of sorption. The magnitudes of ∆G° suggest that ion exchange is the primary sorption mechanism.

Physicochemical characterization of the retardation of aqueous Cs+ ions by natural kaolinite and clinoptilolite minerals

“…The R d values corresponding to sorption of Cs + on kaolinite and clinoptilolite at temperatures of 25 and 60 • C at various initial concentrations and a mixing period of 48 h are given in Table 3. It might be interesting to note the R d values of Cs + sorption on kaolinite obtained in this study using AAS measurements are close the values that we have obtained in an earlier study performed using the radiotracer method [9]. The R d values were used in the calculation of the enthalpy change of sorption, H 0 , and the Gibbs energy of sorption, G 0 , by applying the equations Table 4 gives the values of H 0 and G 0 obtained using the above equations after they were averaged over the entire concentration range.…”

“…The parallel increase in the Cs + mobility within the solution-which could make a positive contribution to sorption-is expected to be insignificant because the ion already possesses a high mobility due to the weak hydration forces of water molecules the thing caused by the low charge density (charge/size) of Cs + ions. The values obtained for the kaolinite case are close to our earlier findings obtained using the radiotracer technique over a wider range of concentration [9]. For both minerals, the obtained results are within the energy range 8-16 kJ/mol, which corresponds to ion-exchange-type sorption mechanism [24].…”

“…So far, a variety of studies have been devoted to characterizing various aspects of the sorption behavior of Cs + ion on kaolinite and on clinoptilolite, using a variety of characterization techniques [9][10][11][12][13][14][15][16][17][18]. In our earlier studies, the retention capacity of kaolinite toward Cs + was studied and compared with that of other clay minerals [9].…”

“…In our earlier studies, the retention capacity of kaolinite toward Cs + was studied and compared with that of other clay minerals [9]. A depth profiling study was also carried out to reveal the distribution of Cs + across the surface of kaolinite [10].…”

A characterization study of some aspects of the adsorption of aqueous Co2+ ions on a natural bentonite clay

“…Hence for the intrinsic sorption reaction to take place, the cation must first undergo partial dehydration in a way that facilitates its migration through the solution to the sites on the sorbent. Based on this and depending on some of our earlier studies, we may conclude, as a first approximation, that cations with relatively low hydration enthalpies (low charge/size ratio, e.g., Cs + ) will demonstrate observed exothermic sorption behavior [12], while cations of higher charge/size ratio (e.g., Sr 2+ , Co 2+ ) will generally show observed endothermic sorption behavior [4,10]. Based on the above statements, the values of H o int could essentially be greater in magnitude than the reported values of H o obs .…”